This invention relates to electronic clinical thermometers of the temperature-estimating type.
Electronic clinical thermometers are roughly divided into two categories. Thermometers of one of the categories are adapted to directly display the temperature of its temperature-measuring element inside a temperature-measuring part. With a thermometer of this type, its temperature-measuring part is placed under the arm or inside the mouth where temperature is intended to be measured, and the measured temperature when it stops rising, or the equilibrium temperature, is considered to be the body temperature at the desired body part. It is generally considered to take about 5 minutes to reach an equilibrium temperature if such a thermometer is placed in the mouth and more than 10 minutes if it is inserted under the arm. Some thermometers of this type are adapted to activate a buzzer when the temperature rise becomes smaller than a specified value and to end the measurement of temperature. With such a thermometer, the measurement may be completed within 3-5 minutes but the actually measured temperature is somewhat lower than the equilibrium temperature.
Japanese Patent Publications Tokkai 52-75385, 55-78220 and 59-187233 and Tokko 7-111383 have disclosed electronic clinical thermometers of the temperature-estimating type adapted to display an estimated equilibrium temperature by extracting the relationship between the characteristics of the temperature-change curve and the equilibrium temperature by a statistical method or from a heat transfer equation, calculating a correction value based on such extracted relationship and adding this calculated value to the current temperature value actually being measured. Thermometers of this type display an estimated result in 1-2 minutes after the measurement is started.
Prior art thermometers of this type make an estimate on the basis of a measured temperature value and the slope of its rise at a certain point in time, or by deriving a heat transfer equation for a situation where a very small object has been heated and carrying out an analysis by a curve approximation method. By such methods, the earlier measured values of the temperature curve are essentially not utilized and only its portion after some length of time has already passed or the transfer of heat from an internal point in the live body to its surface is considered. In other words, the earlier portion was not used in the analysis because it is easily influenced by the initial condition of the temperature-measuring part and the skin surface and such conditions are unstable.
With prior art thermometers of this type, the accuracy of estimate was generally poor especially if the time of measurement was short because the effects of the initial conditions were ignored. For this reason, the user had to wait until the effects of the initial conditions would disappear for obtaining an accurate result. A measurement time of about 60-120 seconds is usually required with a prior art thermometer of this type.